When adding a box collider boat starts moving?

I’m making a boat game, but now when i add a box collider so my bullets can hit him, the boat starts moving! i’ve just ajusted the size of the box with the size of the boat! can anyone tell me what is the problem?

Presuming you have a rigidbody set to isKinematic = false then the collider you have added is acting as part of the structure of the boat. I suggest you set the new collider to isTrigger=true and use the trigger functions to detect the bullet collision.